Hello
I just connect vm140 to potentiometer but data results are unstable. i used AD1 analog inputs , GND and DA2 output 5v.
10k ohm potentiometer.
I will be grateful for your reply.
Regards
Some interference to the wires can cause the unstability.
Please use very short wires - especially the wire to the AD1 input must be short.
You may also use shielded cables. Connect the shield to the GND terminal on VM140.
You may also connect a capacitor e.g. 1uF (or more) between the AD1 input and GND to reduce the electrical noise.
Another possible source of the instability could be noise on the board itself. I experience the same on K8055(N) boards that I converted to PIC18F.
The PIC on the VM140 seems to use the supply voltage as reference voltage for ADC. At 10 bits resolution a one bit error is only 5 mV. Using an Oscilloscope I see noise of more than 20 mV on my K8055(N) boards. The VM140 seems to have a few more noise filtering capacitors, so it probably does better. But using the supply rails as reference voltage will never achieve a result as good as using a separate, stabilized and “clean” reference voltage on the dedicated Vref pins.
Unfortunately installed a shielded cable on the potentiometer. Jumping settings decreased to 10%. It is a chance for improvement?
Potentiometer is mounted on the motor shaft. The whole acts as a servo. But jumping all interfere with our setup. Sorry for language.
Regards
[quote=“baretz81”]Potentiometer is mounted on the motor shaft. The whole acts as a servo. But jumping all interfere with our setup. Sorry for language.
Regards[/quote]
Since these cards take a voltage on the ADC inputs, this means that if you are using a potentiometer, then you also must have some power source for it. What is that power source and how stable is it?
Thanks for the reply.
I take electricity from vellmana 5v analog output.
[quote=“baretz81”]Thanks for the reply.
I take electricity from vellmana 5v analog output.[/quote]
That should work (for some definition of work).
So you have a motor, probably with some reduction gear. I assume the K8055 is controlling that motor with an H-Bridge for left/right. And you are using a potentiometer to figure out the current angular position of the axle.
Is that right so far? If so, are you taking the time delays in communication to the K8055 and back into account?
I use k8061 with ac inverter and motor to the gearbox. Inverter cables are shielded, as well as the potentiometer cable.
k8061 controls the motor via the inverter analog speed and digital direction.
I am working on xsim. Unfortunately, the data from the potentiometer heaving about 5%. This prevents the precise motor control.
Regards
Well, the K8061 is very similar. It has a PIC that does USB 2.0. The communication delays should be similar to a K8055N, but they are definitely there.
Have you checked with an Oscilloscope that these variations in voltage aren’t what really happens on the analog input?
hello
I make a test. Without inverter displays are perfectly stable. Conclusion is that the inverter is causing interference. Do you have any idea how to remove the noise inverter? LG iGa5.
I have shielded cables but it’s definitely not enough.
Regards
Good job on the investigation.
Unfortunately power inverters as well as electric motors produce rather strong electromagnetic interference. With your setup, shielding and/or twisted pair cables is the best you can do. Route those cables as far away as possible from those EMI sources.
This is one of the reasons why real servos use stepper motors. They only need to figure out the initial position on start up. After that it is simply counting the steps. I plan on playing with a rotation detector some day. The little sensors found in old computer mice (the ones with the rubber ball). Those sensors consist of two infrared light barriers and a slotted wheel. The ones I found in an old Logitech mouse seem to divide a 360 degree turn into 256 steps that can be counted up/down. Depending on the speed, your servo is turning, this may or may not be a solution. You would still use the potentiometer to get the position at the beginning or for recalibration.
How fast can your setup turn end to end?
Another idea is to not just use a single reading as the value, but rather put measured values into a round robin array and use the average of that. This will of course result in some more delay of the detected position, depending on the size of that array needed to smooth out the noise.
Out of curiosity, what type of simulator are you building?
Hello
It builds cars and aviation simulators. Until now I used the 24v servo linear actuators. Unfortunately, their strength is too low for use in large platforms Stuart. That’s why I became interested in ac motors.
Can i use encoder instead potentiometer on vm140?
And if yes can you tell me which encoder?
Regards
[quote=“baretz81”]Can i use encoder instead potentiometer on vm140?
And if yes can you tell me which encoder?
Regards[/quote]
That is why I was asking about the rotational speed of your setup. Standard quadrature rotary encoders usually have settings between 32 and 256 PPR. You probably want the 256 steps resolution in your case. When using 256 PPR it would mean that at a speed of 1 rotation per second, there would be 256 state changes on the input ports every second, or roughly a state change every 4ms. I believe the VM140 can read as fast as 2ms or even faster, so that “may” work. I would not try to go any faster with a quadrature encoder directly connected to that card.